124 RAPID POPULATION GROWTH-II countries have achieved levels of mortality almost certainly far below those ever achieved before in human society. In the less developed countries, death rates are falling far more rapidly than they did historically in the more developed countries. Since World War II, reduction in mortality has become worldwide, aside from temporary reverses as the result of war and civil disorder. Further gains are clearly possible, notably in the less developed nations, and indeed great progress is being made. Between 1960 and 1965 the estimated crude death rate (annual deaths per 1,000 population) in the less developed regions as a whole dropped from 20-22 to 16-17, and this achievement was solely responsible for the rise in the rate of population growth in these regions from 20-22 to 24 per 1,000. The estimated annual birth rate for the less developed regions remained about constant: 41-42 in 1960 and 4041 in 1965(2). In the one third of the world that has experienced major economic and social advance the progressive reduction of the death rate has been followed by reduction in the birth rate. In the early stages this was ascribed to many causes, biological, psychological, and nutritional; but it is now generally recognized that the chief factor in reduction of the birth rate has been the voluntary practice of birth control, including induced abortion. Although there remain great advances to be made in reducing or postponing deaths, the less predictable factor in national population growth has become the level and trends in the birth rate. The developed countries, with relatively low birth rates, also have relatively low rates of population growth. In these countries the excess of births over deaths is commonly 1 percent or less per year,* and in the absence of large-scale international migration, their rates of population growth are at this level. Continuation of this 1 percent rate of national population growth will, of course, create problems in the developed areas, although probably of a lesser magnitude than those created by the concentration of population in major metropolitan areas. In the less developed world, however, the problem is more urgent, owing to the unique size and rate of population growth involved. Because of the high birth rate, the annual rate of natural increase is over 2 percent in Asia, 2.5 percent in Africa, and 3 percent in Latin America.t According to the theory of the demographic transition, one would expect the present less developed countries to follow the experience of western countries in reduction of the birth rate. This must occur if there is to be a humane solution of problems of population growth. There is general agreement that birth rates will drop if these countries achieve major socioeconomic *As of 1968 averaging 0.8 percent in Europe, 0.8 percent in the United Slates, 1 percent in the Soviet Union, 1 percent in Canada, and somewhat higher in Japan, Australia. New Zealand. Argentina, and Urueuav.